A new synthetic method for preparing phosphorus imidate esters has been developed which may enable us to prepare potentially important anti-tumor agents and esterase inhibitors. The generality of the synthetic method and the chemistry of the imidate esters will be further investigated to assess the possible biological use and functions of these compounds. Two general approaches will be employed in the actual design and synthesis of drugs; (1) chemically converting compounds of known importance to imidate derivates which would increase the selectivity of the medicinal and (2) preparing imidates which are structurally and chemically analogous to known biologically important compounds. Finally, these imidate esters will be used to probe the nature of the active site in the enzyme cholinesterase.